Turbulence and secondary motions in square duct flow

We study turbulent flows in pressure-driven ducts with square cross-section through direct numerical simulation in a wide enough range of Reynolds number to reach flow conditions which are representative of fully developed turbulence. Numerical simulations are carried out over extremely long integration times to get adequate convergence of the flow statistics, and specifically high-fidelity representation of the secondary motions which arise. The intensity of the latter is found to be in the order of 1-2% of the bulk velocity, and unaffected by Reynolds number variations. The smallness of the mean convection terms in the streamwise vorticity equation points to a simple characterization of the secondary flows, which in the asymptotic high-Re regime are found to be approximated with good accuracy by eigenfunctions of the Laplace operator. Despite their effect of redistributing the wall shear stress along the duct perimeter, we find that secondary motions do not have large influence on the mean velocity field, which can be characterized with good accuracy as that resulting from the concurrent effect of four independent flat walls, each controlling a quarter of the flow domain. As a consequence, we find that parametrizations based on the hydraulic diameter concept, and modifications thereof, are successful in predicting the duct friction coefficient

Ultra-high temperature spark plasma sintering of α-SiC

Ultra High Temperature SPS (UHTSPS) was used to sinter pure α-SiC at 2450 ᵒC. Such a high temperature and partial vacuum conditions promoted SiC sublimation and condensation reactions. In the presence of an electric field, materials with graded porosity could be produced by using UHTSPS. At high temperature, the condensation of the gaseous species was controlled by the polarity of the applied electric field. Preferential condensation of SiC occurred on the negative electrode (cooler surface) due to the Peltier effect associated with the n-type thermoelectric behaviour of SiC. In absence of an electric field, condensation was driven by gravity and it resulted in dense SiC monoliths.S.G. was supported by Grant no. EP/K008749/1 (Material Systems for Extreme Environments) from Engineering and Physical Sciences Research Council (EPSRC). T.S. was supported by FP7 2007–2013 (ADMACOM) a European Community׳s 7th framework Programme

Towards an expanded model of litigation

Introduction: The call for contributions for this workshop describes the important new challenges for the legal search community this domain brings. Rather than just understanding the challenges this domain poses in terms of their technical properties, we would like to suggest that understanding these challenges as socio-technical challenges will be important. That is, as well as calling for research on a technical level to address these challenges we are also calling for work to understand the social practices of those involved in e-discovery (ED) and related legal work. A particularly interesting feature of this field is that it is likely that search technologies will (at least semi-)automate responsiveness review in the relatively near term and this will change the way that the work is organised and done in many ways – offering new possibilities for new ways of organising the work. As well as designing those technologies for automating responsiveness review we need to be envisioning how the work will be done in the future, how these technologies will impact the organisation of the case and so on. In this position paper we therefore outline the importance of understanding the wider social context of ED when designing tools and technologies to support and change the work. We would like to reinforce and expand on Conrad’s call for IR researchers to understand just what ED entails [2], include the stages that come both before and after core retrieval activities. The importance of considering the social aspects of work in the design of the technology has been established for some time. Ushering in this ‘turn to the social,’ and focusing on interface design, Gentner and Grudin [4] described how the GUI has already changed from an interface for engineers, representing the engineering model of the machine to one that supported single ‘everyman’ users (based on ideas from psychology). From then onwards the interface has evolved to support groups of users, taking into account the social and organisational contexts of use. This has particular resonance for the design of ED technologies: during ED in particular and the wider legal process there are often many lawyers involved – reviewing documents, determining issues, etc. Even if the way that their work is organised currently is not seen as collaborative in the traditional sense – with individual lawyers working on individual document sets to review them - their work needs to be coordinated and it seems likely that their work could be enhanced by, for example, knowledge of what their colleagues had found, how the case was shaping up, new key terms and facts turned up and so on. Work is often modelled for the purposes of design using process models, but this misses out on the richness and variety actually found when one examines how the work is carried out [3]. Technologies which strictly enforce the process models can often hinder the work, or end up being worked around as was the case with workflow systems since people interpret processes very flexibly to get the work done ([1], [3]). Other studies in other fields have found similar problems when systems are designed on for example cognitive models of how the work is done; they often do not take into account the situated nature of the work and thus they can be very difficult to use [5]. We believe, like [2], that a clear understanding of the social practices of ED is vital for the creation of high-quality, meaningful tools and technologies. We furthermore propose that work practice studies, to be used in combination with other methods, are a central part of getting the detailed understanding of the work practices central to designing useful and intelligent tools. Work practice studies would involve ethnographies, consisting primarily of observation, undertaken of practitioners engaging in the work of ED

On mixing angles and magnetic moment of heavy tau neutrino

If the magnetic moment of unstable tau neutrinos with the mass of $O$(MeV) is in the region of $10^{-8}\mu_{B} \lesssim \mu_{\nu_{\tau}} \lesssim 10^{-6}\mu_{B}$, it is compatible with the present experimental and cosmological bounds. It is pointed out here, that if the tau neutrino has such a large magnetic moment and can oscillate into a neutrino of another flavour the results from $\nu e$ scattering experiment at LAMPF constrain the tau neutrino mixing angles to $sin^{2}2\theta_{e \tau} \lesssim 2\times 10^{-6} - 2\times 10^{-2}$ and $sin^{2}2\theta_{\mu\tau} \lesssim 10^{-6} - 10^{-2}$ depending on the magnetic moment value in the allowed region.Comment: 5 pages, LaTe

Heat transfer and wall temperature effects in shock wave turbulent boundary layer interactions

Direct numerical simulations are carried out to investigate the effect of the wall temperature on the behavior of oblique shock-wave/turbulent boundary layer interactions at freestream Mach number $2.28$ and shock angle of the wedge generator $\varphi = 8^{\circ}$. Five values of the wall-to-recovery-temperature ratio ($T_w/T_r$) are considered, corresponding to cold, adiabatic and hot wall thermal conditions. We show that the main effect of cooling is to decrease the characteristic scales of the interaction in terms of upstream influence and extent of the separation bubble. The opposite behavior is observed in the case of heating, that produces a marked dilatation of the interaction region. The distribution of the Stanton number shows that a strong amplification of the heat transfer occurs across the interaction, and the maximum values of thermal and dynamic loads are found in the case of cold wall. The analysis reveals that the fluctuating heat flux exhibits a strong intermittent behavior, characterized by scattered spots with extremely high values compared to the mean. Furthermore, the analogy between momentum and heat transfer, typical of compressible, wall-bounded, equilibrium turbulent flows does not apply for most part of the interaction domain. The pre-multiplied spectra of the wall heat flux do not show any evidence of the influence of the low-frequency shock motion, and the primary mechanism for the generation of peak heating is found to be linked with the turbulence amplification in the interaction region.Comment: submitted to PRFluid

Hard Cosmic Ray Sea in the Galactic Center: a consistent interpretation of H.E.S.S. and Fermi-LAT γ\gamma-ray data

We present a novel interpretation of the gamma-ray diffuse emission measured by H.E.S.S. in the Galactic Center (GC) region and the Galactic ridge. Our starting base is an updated analysis of PASS8 Fermi-LAT data, which allows to extend down to few GeV the spectra measured by H.E.S.S. and to infer the primary CR radial distribution above 100 GeV. We compare those results with a CR transport model assuming a harder scaling of the diffusion coefficient with rigidity in the inner Galaxy. Such a behavior reproduces the radial dependence of the CR spectral index recently inferred from Fermi-LAT measurements in the inner GP. We find that, in this scenario, the bulk of the Galactic ridge emission can be naturally explained by the interaction of the diffuse, steady-state Galactic CR sea interacting with the gas present in the Central molecular zone. The evidence of a GC PeVatron is significantly weaker than that inferred adopting a conventional (softer) CR sea.Comment: Oral contribution to the International Cosmic Ray Conference (ICRC 2017), 12-20 July 2017, Bexco, Busan, Kore

Taranto: a flickering landscape of illusory progress, vanished hope, and invisible beauty

The article investigates the difficult and controversial landscape of Taranto, a recently industrialised city of southern Italy, which in the last 70 years has undergone dramatic changes. We analyse what the landscape is in material, cultural, and symbolic terms, what it does, and what it means in and for Taranto. In particular, by analysing bibliographic, cartographic, and audiovisual sources, we trace the evolution of contemporary Taranto, indicating the main factors which enabled its material transformation during the second half of the twentieth century. Then, we reflect on how the landscape has been shaped in different times and at different scales through dominant narratives and counter-narratives. Finally, we identify specific elements of Taranto's landscape and their symbolic meaning. The study offers a paradigmatic case of a flickering landscape, modified by political forces and cultural constructs

Violent political action during the European economic crisis: an empirical investigation of four theoretical paradigms from social movement research

The recent economic crisis has witnessed a surge in demonstrations and other protest actions all over Europe, while in the most affected countries—such as Greece—the use of personal violence and damage of property became an everyday phenomenon. What are the drivers of violent political action in times of crisis? How do these drivers interact? And to what extent does context matter? These questions are examined in the light of a new and original survey data set carried out across nine European countries, all affected to different degrees by the financial crisis. Four theoretical paradigms from social movement research that account for violent political action are examined. This study looks beyond the staple explanations of relative deprivation and resource mobilisation, expands the analysis to include a relational approach—namely, conflictual irrelevance—and explores the soundness of an integrative approach that attempts to reconcile the traditional divide between grievance and resource-based models. By measuring actual behaviour rather than merely intention, the article furthermore contributes to the discussion over the participation of individuals in violent activism and gives empirical support to the dual-pathways model of collective action for the understanding of violent political action during times of crisis

Direct numerical simulation of developed compressible flow in square ducts

We carry out direct numerical simulation of compressible square duct flow in the range of bulk Mach numbers M b =0.2−3, and up to friction Reynolds number Re τ =500. The effects of flow compressibility on the secondary motions are found to be negligible, with the typical Mach number associated with the cross-stream flow always less than 0.1. As in the incompressible case, we find that the wall law for the mean streamwise velocity applies with good approximation with respect to the nearest wall, upon suitable compressibility transformation. The same conclusion also applies to a passive scalar field, whereas the mean temperature does not exhibit inertial layers because of nonuniformity of the aerodynamic heating. We further find that the same temperature/velocity relation that holds for planar channels is applicable with good approximation for square ducts, and develop a similar relation between temperature and passive scalars

Ultrafast-Contactless Flash Sintering using Plasma Electrodes

This paper presents a novel derivative of flash sintering, in which contactless flash sintering (CFS) is achieved using plasma electrodes. In this setup, electrical contact with the sample to be sintered is made by two arc plasma electrodes, one on either side, allowing current to pass through the sample. This opens up the possibility of continuous throughput flash sintering. Preheating, a usual precondition for flash sintering, is provided by the arc electrodes which heat the sample to 1400 °C. The best results were produced with pre-compacted samples (bars 1.8 mm thick) of pure B(4)C (discharge time 2s, current 4A) and SiC:B(4)C 50 wt% (3s at 6A), which were fully consolidated under a heating rate approaching 20000 °C/min. For the composite a cylindrical volume of 14 mm(3) was sintered to full density with limited grain growth